1. Field of the Invention
The present invention relates to a screw compressor having a pair of rotors rotatable around its rotary axes.
2. Description of the Related Art
FIG. 5 shows a conventional screw compressor including a pair of male and female rotors J1, J2 having spiral teeth that are provided to be engaged with each other (e.g., JP-A-2005-220785). In this screw compressor, by rotating the male rotor J1 and the female rotor J2 in a housing J6, gas is drawn from a suction port J6a into a compression chamber formed between tooth tips and tooth roots (grooves) of the rotors J1, J2. Then, the gas compressed in the compression chamber is discharged from a discharge port J6b of the housing.
In this screw compressor, after the volume of the compression chamber is gradually expanded from the zero, the compression chamber is made to communicate with the suction port J6a. Therefore, a negative pressure is generated in the compression chamber before being communicated with the suction port J6a (i.e., the area X shown in FIG. 5), thereby causing a drive loss during the rotation of the rotors J1, J2. In order to prevent the generation of the pressure loss in the compression chamber, a groove for communicating the compression chamber and the suction port J6a may be provided on an end surface of the rotors J1, J2.
However, when the suction port J6a is provided in the housing J6 to be opened in a radial direction, a gas flow Y, pushed toward the suction port J6a by the rotation of the rotors J1, J2, is generated toward radial outside of the rotors J1, J2, thereby this gas flow Y disturbs a gas flow from the suction port J6a into a groove J6c shown in FIG. 6. Accordingly, it is impossible to sufficiently reduce the negative pressure generated in the compressor chamber before being communicated with the suction port J6a. 